Graphene Hybrids for Advanced Interface

www.acsnano.org

Downloaded via KAOHSIUNG MEDICAL UNIV on September 21, 2018 at 23:06:31 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

MoS2 Quantum Dot/Graphene Hybrids for Advanced Interface Engineering of a CH3NH3PbI3 Perovskite Solar Cell with an Efficiency of over 20% Leyla Najafi,†,# Babak Taheri,‡,# Beatriz Martín-García,† Sebastiano Bellani,† Diego Di Girolamo,‡ Antonio Agresti,‡ Reinier Oropesa-Nuñez,†,∥ Sara Pescetelli,‡ Luigi Vesce,‡ Emanuele Calabrò,‡ Mirko Prato,⊥ Antonio E. Del Rio Castillo,† Aldo Di Carlo,*,‡,§ and Francesco Bonaccorso*,†,∥ †

Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy C.H.O.S.E. (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy ∥ BeDimensional Srl., Via Albisola 121, 16163 Genova, Italy ⊥ Materials Characterization Facility, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy § L.A.S.E.−Laboratory for Advanced Solar Energy, National University of Science and Technology “MISiS”, Leninskiy Prosect 6, 119049 Moscow, Russia ‡

S Supporting Information *

ABSTRACT: Interface engineering of organic−inorganic halide perovskite solar cells (PSCs) plays a pivotal role in achieving high power conversion efficiency (PCE). In fact, the perovskite photoactive layer needs to work synergistically with the other functional components of the cell, such as charge transporting/ active buffer layers and electrodes. In this context, graphene and related two-dimensional materials (GRMs) are promising candidates to tune “on demand” the interface properties of PSCs. In this work, we fully exploit the potential of GRMs by controlling the optoelectronic properties of molybdenum disulfide (MoS2) and reduced graphene oxide (RGO) hybrids both as hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3)-based PSCs. We show that zero-dimensional MoS2 quantum dots (MoS2 QDs), derived by liquid phase exfoliated MoS2 flakes, provide both hole-extraction and electron-blocking properties. In fact, on one hand, intrinsic n-type doping-induced intraband gap states effectively extract the holes through an electron injection mechanism. On the other hand, quantum confinement effects increase the optical band gap of MoS2 (from 1.4 eV for the flakes to >3.2 eV for QDs), raising the minimum energy of its conduction band (from −4.3 eV for the flakes to −2.2 eV for QDs) above the one of the conduction band of MAPbI3 (between −3.7 and −4 eV) and hindering electron collection. The van der Waals hybridization of MoS2 QDs with functionalized reduced graphene oxide (f-RGO), obtained by chemical silanizationinduced linkage between RGO and (3-mercaptopropyl)trimethoxysilane, is effective to homogenize the deposition of HTLs or ABLs onto the perovskite film, since the two-dimensional nature of RGO effectively plugs the pinholes of the MoS2 QD films. Our “graphene interface engineering” (GIE) strategy based on van der Waals MoS2 QD/graphene hybrids enables MAPbI3-based PSCs to achieve a PCE up to 20.12% (average PCE of 18.8%). The possibility to combine quantum and chemical effects into GIE, coupled with the recent success of graphene and GRMs as interfacial layer, represents a promising approach for the development of next-generation PSCs. KEYWORDS: perovskite solar cells, 2D materials, graphene, molybdenum disulfide (MoS2), quantum dots, interface engineering

O

rganic−inorganic halide perovskite solar cells (PSCs) are in the spotlight of photovoltaic (PV) research to rival the leading technologies1−4 (i.e., crystalline © XXXX American Chemical Society

Received: July 22, 2018 Accepted: September 13, 2018

A

DOI: 10.1021/acsnano.8b05514 ACS Nano XXXX, XXX, XXX−XXX

Article

Cite This: ACS Nano XXXX, XXX, XXX−XXX

Article

ACS Nano

Figure 1. (a) Sketch of mesoscopic MAPbI3-based PSC exploiting MoS2 QDs:f-RGO hybrids as both HTL and ABL. (b) Scheme of the energy band edge positions of the materials used in the different components of the assembled mesoscopic MAPbI3-based PSC. The energy band edge positions of MoS2 flakes and MoS2 QDs were determined from OAS and UPS measurements detailed in the text, while those of the other materials were taken from the literature: FTO,52 TiO2,52 MAPbI3,134−139 spiro-OMeTAD,52 and Au.52 (c) State-of-the-art and predicted PCE evolution for PSCs, highlighting the synergistic potential of GIE and the formulation of advanced perovskite chemistries.

silicon solar cells5−7 and inorganic thin-film solar cells8,9) since power conversion efficiency (PCE) exceeding 20%10−12 can be obtained by affordable (low-cost and low-temperature) solution processing13−15 with a scaling-up prospective.16−19 Methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3) has been intensively studied as light-harvesting material from the beginning of PSC development,1,2,20−22 and the elemental composition engineering of its chemistry23,24 led to mixed cation and halide PSCs,25 which boosted the certified PCE above 22% (i.e., 22.1%26 and 22.7%10). Although the archetypal MAPbI3 reached a certified maximum efficiency of 19.3%27 (uncertified efficiency exceeding 20%28−31), it still has a benchmarking role for the optimization and/or validation of PSC architectures31−34 due to its historical breakthrough in PV technology over the last years (starting from 2009, with a PCE of 3.8%21).10 In particular, MAPbI3-based PSCs provide a platform to study and design the interfaces between each functional layer of the PSCs,16,35−41 whose carrier transport barriers determine undesirable hysteresis and instability effects in PSCs,33,42−44 both in mesoscopic31,45 and planar structures.45 In fact, the photogenerated carriers have to be transported across the interfaces in the PSC structure,38,46−48 and charge loss can occur due to energy barriers and/or interfacial defects.38,46−48 Therefore, appropriate energy level tailoring at the interfaces is pivotal in (1) increasing open circuit voltage (Voc); (2) facilitating charge transfer and

extraction,49,50 which contribute to increase the short circuit current (Jsc) and fill factor (FF);49,50 (3) eliminating hysteresis phenomena;51−53 and (4) extending the lifetime.54,55 In the run-up to reach the theoretical PCE limit (∼31%)56 of PSCs (practical limits of 29.5%57 with value of 30.5%,58 which have also been reported by considering intrinsic nonradiative recombination processes), graphene and related two-dimensional (2D) materials (GRMs) are emerging as a paradigm shift of interface engineering to boost the PV performance.56,59−73 Actually, the large variety of GRMs offers peculiar (opto)electronic properties74,75 that can be tuned on-demand by means of morphological modification76,77 and chemical functionalization.78−80 Moreover, GRMs can be produced from the exfoliation of their bulk counterpart in suitable solvents81−85 as functional inks.86 The latter can be deposited on different substrates by established large-scale, cost-effective printing/coating techniques,87−90 compatible with solutionbased manufacturing of PSCs.15,91−93 With the aim to deeply exploit the use of 2D materials for engineering the interface of PSCs, herein we report a synergistic quantum-chemical approach for controlling the energy band levels and the thin-film morphology of lowdimensional, van der Waals hybrids between molybdenum disulfide quantum dots (MoS2 QDs) and reduced graphene oxide (RGO) as hole transport layer (HTL) or active buffer layer (ABL) (between the HTL and Au electrode) in B


Article

ACS Nano

Scheme 1. Representative sketches of (a) the functionalization of RGO (structure based on the Lerf−Klinowski model)186 with MPTS; (b) the hybridization of MoS2 QDs and f-RGO.

MoS2 flakes,144 hold optimal electronic structure to effectively extract the photogenerated holes through an electron injection mechanism145−147 from their intrinsic n-type doping148−151induced intraband gap states.152,153 The latter have been reported to be a consequence of the natural presence in MoS2 of sulfur vacancies,153−158 impurities,159,160 and defects.161−164 Quantum confinement effects open the MoS2 optical band gap (from 1.4 eV for the flakes to >3.2 eV for the QDs), raising the minimum energy of the CB of MoS2 (from −4.3 eV for the flakes to −2.2 eV for the QDs) above the energy of the LUMO of MAPbI3 (between −4.0134−137 and −3.7 eV114,138,139), thus blocking electron injection in HTL. Hole-extraction and electron-blocking properties of MoS2 QDs synergistically suppress the interfacial charge recombination losses observed in benchmark devices (fluorine-doped tin oxide (FTO)/ compact TiO2 (cTiO2)/mesoporous TiO2 (mTiO2)/MAPbI3/ 2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD)/Au),34,165 and in previous cell architectures exploiting native MoS2 flakes as ABLs.64,165 With the aim to form homogeneous (i.e., pinhole-free) nanometerthick HTLs, MoS2 QDs, which do not cover totally the MAPbI3 film after their deposition, are hybridized with chemically (3-mercaptopropyl)trimethoxysilane (MPTS)-functionalized RGO (f-RGO) flakes166 (named MoS2 QDs:f-

mesoscopic MAPbI3-based PSCs (Figure 1a). Notably, both 2D MoS2 and RGO have been previously reported as possible HTLs64,72,94−103 or ABLs.64,104,105 However, their intrinsic work function (WF) (typically 4.9,114,115 especially for the doped forms mostly exploited as HTLs114−117) and poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (WF ranging between 5.0 and 5.2 eV118−121). This can limit the hole extraction process.95,122,123 Moreover, the optical band gap (Eg) of both RGO (20% PCE, has been recently achieved by formulating perovskites with mixed cations, i.e., formamidinium (FA), MA, and inorganic species (Cs or Ru).261,262 Oneyear stable PSCs were achieved by engineering an ultrastable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite junction.39 Despite this result, interface engineering of PSCs also affects their stability,16,60,61,69,263 since the diffusion of elemental species such as iodine(I) and metal from the electrode materials (e.g., Au244 or Ag264) has been recently correlated with the degradation of interfaces and the decay of the PV properties.265 In this context, the incorporation of graphene flakes into mTiO2 has been demonstrated to increase the chemical stability of overlying MAPbI3, which exhibited higher crystalline quality compared to that of MAPbI 3 deposited directly onto mTiO269 and a freezed tetragonal phase regardless of the temperature.69 An active buffer layer based on GRMs improved the charge extraction process compared to that of the ABL-free reference, preventing the degradation induced by the diffusion of Au and I.71,104,231,266,267 Although it was not the goal of our work to overcome the intrinsic instability of MAPbI3, the stability of the devices after encapsulation was measured in ISOS-D-1 shelf life aging test protocol268 (Figure 7). After a 1032 h aging test, the ABL-based PSCs exhibited a decrease of PCE of only 13.5%, 11.2%, and 8.8% for MoS2 QDs-, f-RGO-, and MoS2 QDs:f-RGO-based PSCs, respectively. These reduced values are significantly lower than the ones shown by the reference PSC without ABL (24.6%). The improved stability of the ABL-based PSCs compared to the reference PSC is ascribed to the surface passivation of the perovskite layer provided by the ABLs, which mitigate the I migration from the MAPbI3 into the spiro-OMeTAD269 and the formation of Au pathways from the metal electrode to the MAPbI3.270

EXPERIMENTAL METHODS Production of Materials. Graphene oxide was synthesized from graphite flakes (Sigma-Aldrich, +100 mesh ≥75% min) using a modified Hummer’s method.182 Briefly, 1 g of graphite and 0.5 g of NaNO3 (Sigma-Aldrich, reagent grade) were mixed, followed by the dropwise addition of 25 mL of H2SO4 (Sigma-Aldrich). After 4 h, 3 g of KMnO4 (Alpha Aesar, ACS 99%) was added slowly to the above solution, keeping the temperature at 4 °C with the aid of an ice bath. The mixture was let to react at room temperature overnight, and the resulting solution was diluted by adding 2 L of distilled water under vigorous stirring. The sample was filtered and rinsed with H2O. Finally the sample was dried at 110 °C overnight. Reduced graphene oxide was produced by thermal reduction of the as-produced GO180,181 in a quartz tube (120 cm length and 25 mm inner diameter) passing through a three-zone split furnace (PSC 12/--/600H, Lenton, UK). Experimentally, gas flows were controlled upstream by an array of mass flow controllers (1479A, mks, USA). Under a 100 sccm flow of Ar/H2 (90/10%), 100 mg of GO was heated to 100 °C for 20 min to remove the presence of water residuals. Subsequently, a ramp of 20 °C min−1 was used to reach J


Article

ACS Nano 1000 °C and stabilized at this temperature for 2 h. Finally, the oven was left to cool to room temperature. The RGO was functionalized with MPTS (95%, Sigma-Aldrich) in an ethanol (absolute alcohol, ≥99.8%, without additive, SigmaAldrich) solution by reflux at 60 °C for 15 h.166 For this reaction 250 μL of MPTS was added per mg of RGO. After the synthesis, the silane-functionalized RGO material was recovered by centrifugation (9000 rpm) and redispersed in ethanol (EtOH) by vortexing for a second centrifugation (9000 rpm) to remove unreacted silane. A solvent-exchange process184,185,95 was carried out to redisperse the fRGO in IPA at a concentration of 0.4 mg mL−1. Molybdenum disulfide quantum dots were produced through a one-step solvothermal method starting from MoS2 flakes, produced by LPE144 of bulk MoS2 crystals in IPA followed by SBS.172,173 In detail, 30 mg of MoS2 bulk crystal (Sigma-Aldrich) was added to 50 mL of IPA and then ultrasonicated (Branson 5800 cleaner, Branson Ultrasonics) for 8 h. The resulting dispersion was ultracentrifuged (Optima XE-90 ultracentrifuge, Beckman Coulter) for 15 min at 2700g, in order to separate the unexfoliated MoS2 crystals (collected as sediment) from the thinner MoS2 flakes that remain in the supernatant. Then, the sample was refluxed in air under stirring for 24 h at 140 °C. The resulting dispersion was subsequently ultracentrifuged for 30 min at 24600g. Afterward, the supernatant was collected, obtaining the MoS2 QDs dispersion. By evaporating the solvent, a concentration of 0.2 mg mL−1 was obtained. The hybrid dispersion between MoS2 QDs and f-RGO was produced by mixing the as-produced component dispersions in a volume ratio of 1:1 (corresponding to a weight ratio of 1:2). By evaporating the solvent, the concentration was doubled in order to have the same amount of the material compared to the native dispersions. Characterization of Materials. Transmission electron microscopy images were taken with a JEM 1011 (JEOL) TEM (thermionic W filament), operating at 100 kV. Morphological and statistical analysis was carried out by using ImageJ software (NIH) and OriginPro 9.1 software (OriginLab), respectively. The statistical analysis was performed on 50 flakes from the different TEM images collected. The lateral dimension of each flake was calculated as the maximum Feret’s diameter. Samples for the TEM measurements were prepared by drop casting the material dispersions onto ultrathin carbon-coated copper grids rinsed with deionized water and subsequently dried under vacuum overnight. Atomic force microscopy images were taken using a Nanowizard III (JPK Instruments, Germany) mounted onto an Axio Observer D1 (Carl Zeiss, Germany) inverted optical microscope. The AFM measurements were carried out by using PPP-NCHR cantilevers (Nanosensors, USA) with a nominal tip diameter of 10 nm. A drive frequency of ∼295 kHz was used. Intermittent contact mode AFM images (512 × 512 data points) of 2.5 × 2.5 μm2 were collected by keeping the working set point above 70% of the free oscillation amplitude. The scan rate for acquisition of images was 0.7 Hz. Height profiles were processed by using the JPK Data Processing software (JPK Instruments, Germany), and the data were analyzed with OriginPro 9.1 software. Statistical analysis was carried out by means of Origin 9.1 software on multiple AFM images for each sample and calculated on 50 flakes. The samples were prepared by drop-casting the material dispersions onto mica sheets (G250-1, Agar Scientific Ltd., Essex, U.K.) and dried under vacuum. Optical absorption spectroscopy measurements were carried out on material dispersions by using a Cary Varian 5000 UV−vis spectrometer. X-ray photoelectron spectroscopy characterization was carried out on a Kratos Axis UltraDLD spectrometer, using a monochromatic Al Kα source (15 kV, 20 mA). The spectra were taken on a 300 × 700 μm2 area. Wide scans were collected with a constant pass energy of 160 eV and an energy step of 1 eV. High-resolution spectra were acquired at a constant pass energy of 10 eV and energy step of 0.1 eV. The binding energy scale was referenced to the C 1s peak at 284.8 eV. The spectra were analyzed using the CasaXPS software (version 2.3.17). The samples were prepared by drop-casting the material

dispersions onto a Si/SiO2 substrate (LDB Technologies Ltd.) and dried under vacuum. Fourier-transform infrared spectroscopy was performed in a Bruker Vertex 70v (4000−400 cm−1 range, 100 scans). The samples were prepared by drop casting MPTS, RGO, f-RGO, and MoS2 QDs:fRGO films on BaF2 substrates (IR grade, Crystran, IR open window 4000 to 600 cm−1). Ultraviolet photoelectron spectroscopy analysis was performed to estimate the Fermi energy level (EF) of the materials under investigation with the same equipment used for XPS and adopting a He I (21.22 eV) discharge lamp. The EF was measured from the threshold energy for the emission of secondary electrons during He I excitation. A −9.0 V bias was applied to the sample in order to precisely determine the low kinetic energy cutoff. The samples were prepared by drop casting onto 50 nm Au-sputter-coated silicon wafers. Fabrication of Solar Cells. The solar cells containing four devices were fabricated on laser-patterned glass/FTO substrates (Pilkington, 8 Ω □−1), which were washed for 15 min with acetone, ethanol, and deionized water in an ultrasonic bath, respectively. Furthermore, a compact 40 nm TiO2 layer (c-TiO2) was deposited onto the precleaned laser-patterned FTO glass via spray pyrolysis (450 °C) from a solution consisting of 0.16 M diisopropoxytitanium bis(acetylacetonate) (Ti(AcAc)2) and 0.4 M acetyl acetone (AcAc) in ethanol. For the mesoporous TiO2 (m-TiO2) layer, anatase TiO2 nanoparticle paste (30NRD, GreatCell SolarDyesol) was dissolved in ethanol by stirring at a w/w ratio of 1:6. A mesoporous layer was deposited onto c-TiO2 by spin-coating 140 μL of paste at 3000 rpm for 15 s and subsequently sintered at 480 °C for 30 min. Successively, a MAPbI3 perovskite absorber layer was deposited by a solvent engineering method. Briefly 717.76 mg mL−1 of PbI2 and 247.56 mg mL−1 of CH3NH3I were dissolved in DMF/DMSO (8:1, v/v) by stirring for 24 h at room temperature to obtain the perovskitebased solution. A 70 μL amount of the perovskite solution was spin coated on the mesoporous layer with two-step spinning, first 1000 rpm for 10 s and then 5000 rpm for 45 s. Just 34 s before the end of the second spin-coating step, 0.7 mL of diethyl ether was dropped on the substrates. Subsequently, the perovskite layer was treated with a double-step annealing process, performed at 50 °C for 2 min and then at 100 °C for 10 min. After the heat treatment of the perovskite layer, the 2D materials dispersed in IPA were deposited by automated spray-coating equipment (Aurel) onto the perovskite layer by using N2 flow (see SI, for the spray parameter settings, Figure S12). A 100 μL amount of the HTL material solution containing spiro-OMeTAD (73.5 mg.mL−1, Borun sublimed grade >99.8%) in chlorobenzene (Sigma-Aldrich) doped with 26 μL of tert-butylpyridine (TBP, SigmaAldrich, 96%), 16.6 μL of lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI, Sigma-Aldrich, 99.95%) of stock solution (520 mg in 1 mL acetonitrile, Sigma-Aldrich), and 7.2 μL of cobalt(III) complex solution (FK209 from Lumtec) was deposited by spin coating at 2000 rpm for 20 s. Finally, 80 nm of Au counter electrode was deposited by thermal evaporation in high-vacuum conditions (10−6 mbar). For the shelf life tests, the device were encapsulated following the protocol previously reported in ref 269. Characterization of Solar Cells. Scanning electron microscopy analysis of solar cells was performed using a Helios Nanolab 600 DualBeam microscope (FEI Company) and 10 kV and 0.2 nA as measurement conditions. For the EDX spectra acquisition and analysis on the solar cells we used the microscope combined with an X-Max detector and INCA system (Oxford Instruments) and 15 kV and 0.8 nA as measurement conditions. The samples were imaged without any metal coating or pretreatment. To evaluate the layered stack of the solar cell by cross section, the samples were prepared using focused ion beam coupled to the microscope. Current−voltage characteristics of masked and encapsulated devices were acquired in air atmosphere by using a solar simulator (ABET Sun 2000, class A) at AM1.5 and 100 mW cm−2 illumination conditions, calibrated with a certified reference Si cell (RERA Solutions RR-1002). Devices were not preconditioned before the I−V measurements. I−V scans were performed by using a scan rate of 20 K


Article

ACS Nano mV s−1. Incident photon to current conversion efficiency spectra acquisition was carried out by means of a homemade setup composed by a monochromator (Newport, model 74000) coupled with a Xe lamp (Oriel Apex, Newport) and a source meter (Keithley, model 2612). A homemade LabVIEW program controlled the spectra acquisition. Shelf life test was carried out on encapsulated devices (by following the indications of the ISOS-D-1 shelf life aging test protocol).272 In particular, the devices were kept in dark, dry conditions (relative humidity 1,000 h Operational Stability. Nat. Energy 2018, 3, 68−74. (56) Sha, W. E. I.; Ren, X.; Chen, L.; Choy, W. C. H. The Efficiency Limit of CH3NH3PbI3 Perovskite Solar Cells. Appl. Phys. Lett. 2015, 106, 221104. (57) Baloch, A. A. B.; Hossain, M. I.; Tabet, N.; Alharbi, F. H. Practical Efficiency Limit of Methylammonium Lead Iodide Perovskite (CH3NH3PbI3) Solar Cells. J. Phys. Chem. Lett. 2018, 9, 426− 434. (58) Pazos-Outón, L. M.; Xiao, T. P.; Yablonovitch, E. Fundamental Efficiency Limit of Lead Iodide Perovskite Solar Cells. J. Phys. Chem. Lett. 2018, 9, 1703−1711. (59) Agresti, A.; Pescetelli, S.; Palma, A. L.; Del Rio Castillo, A. E.; Konios, D.; Kakavelakis, G.; Razza, S.; Cinà, L.; Kymakis, E.; Bonaccorso, F.; Di Carlo, A. Graphene Interface Engineering for M


Article

ACS Nano Perovskite Solar Modules: 12.6% Power Conversion Efficiency over 50 cm2 Active Area. ACS Energy Lett. 2017, 2, 279−287. (60) Agresti, A.; Pescetelli, S.; Taheri, B.; Del Rio Castillo, A. E.; Cina, L.; Bonaccorso, F.; Di Carlo, A. Graphene−Perovskite Solar Cells Exceed 18% Efficiency: A Stability Study. ChemSusChem 2016, 9, 2609−2619. (61) Kakavelakis, G.; Maksudov, T.; Konios, D.; Kioseoglou, G.; Stratakis, E.; Kymakis, E. Efficient and Highly Air Stable Planar Inverted Perovskite Solar Cells with Reduced Graphene Oxide Doped PCBM Electron Transporting Layer. Adv. Energy Mater. 2017, 7, 1602120. (62) Agresti, A.; Pescetelli, S.; Cina, L.; Dimitrios, K.; Kakavelakis, G.; Kymakis, E.; Di Carlo, A. Efficiency and Stability Enhancement in Perovskite Solar Cells by Inserting Lithium-Neutralized Graphene Oxide as Electron Transporting Layer. Adv. Funct. Mater. 2016, 26, 2686−2694. (63) Cho, K. T.; Grancini, G.; Lee, Y.; Konios, D.; Paek, S.; Kymakis, E.; Nazeeruddin, M. K. T. Beneficial Role of Reduced Graphene Oxide for Electron Extraction in Highly Efficient Perovskite Solar Cells. ChemSusChem 2016, 9, 3040−3044. (64) Capasso, A.; Matteocci, F.; Najafi, L.; Prato, M.; Buha, J.; Cinà, L.; Pellegrini, V.; Di Carlo, A.; Bonaccorso, F. Few-Layer MoS2 Flakes as Active Buffer Layer for Stable Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1600920. (65) Shan, C.; Gaoquan, S. Two-Dimensional Materials for Halide Perovskite-Based Optoelectronic Devices. Adv. Mater. 2017, 29, 1605448. (66) Van Le, Q.; Choi, J.-Y.; Kim, S. Y. Recent Advances in the Application of Two-Dimensional Materials as Charge Transport Layers in Organic and Perovskite Solar Cells. FlatChem. 2017, 2, 54− 66. (67) Chen, W.; Li, K.; Wang, Y.; Feng, X.; Liao, Z.; Su, Q.; Lin, X.; He, Z. Black Phosphorus Quantum Dots for Hole Extraction of Typical Planar Hybrid Perovskite Solar Cells. J. Phys. Chem. Lett. 2017, 8, 591−598. (68) Muduli, S. K.; Varrla, E.; Kulkarni, S. A.; Han, G.; Thirumal, K.; Lev, O.; Mhaisalkar, S.; Mathews, N. 2D Black Phosphorous Nanosheets as a Hole Transporting Material in Perovskite Solar Cells. J. Power Sources 2017, 371, 156−161. (69) Biccari, F.; Gabelloni, F.; Burzi, E.; Gurioli, M.; Pescetelli, S.; Agresti, A.; Del Rio Castillo, A. E.; Ansaldo, A.; Kymakis, E.; Bonaccorso, F.; Di Carlo, A. Graphene-Based Electron Transport Layers in Perovskite Solar Cells: A Step-Up for an Efficient Carrier Collection. Adv. Energy Mater. 2017, 7, 1701349. (70) Ruina, D.; Yangyang, W.; Jie, W.; Xianyu, D. Metal−OrganicCompound-Modified MoS2 with Enhanced Solubility for HighPerformance Perovskite Solar Cells. ChemSusChem 2017, 10, 2869− 2874. (71) Kakvelakis, G.; Paradisanos, I.; Paci, B.; Generosi, A.; Papachatzakis, M.; Maksukov, T.; Najafi, L.; Del Rio Castillo, A. E.; Kioseoglou, G.; Stratakis, E.; Bonaccorso, F.; Kymakis, E. Extending the Continuous Operating Lifetime of Perovskite Solar Cells with a Molybdenum Disulfide Hole Extraction Interlayer. Adv. Energy Mater. 2018, 8, 1702287. (72) Dasgupta, U.; Chatterjee, S.; Pal, A. J. Thin-Film Formation of 2D MoS2 and Its Application as a Hole-Transport Layer in Planar Perovskite Solar Cells. Sol. Energy Mater. Sol. Cells 2017, 172, 353− 360. (73) Kuila, T.; Bose, S.; Mishra, A. K.; Khanra, P.; Kim, N. H.; Lee, J. H. Chemical Functionalization of Graphene and Its Applications. Prog. Mater. Sci. 2012, 57, 1061−1105. (74) Ferrari, A. C.; Bonaccorso, F.; Fal’ko, V.; Novoselov, K. S.; Roche, S.; Bøggild, P.; Borini, S.; Koppens, F. H. L.; Palermo, V.; Pugno, N.; Garrido, J. A.; Sordan, R.; Bianco, A.; Ballerini, L.; Prato, M.; Lidorikis, E.; Kivioja, J.; Marinelli, C.; Ryhänen, T.; Morpurgo, A.; et al. Science and Technology Roadmap for Graphene, Related TwoDimensional Crystals, and Hybrid Systems. Nanoscale 2015, 7, 4598− 4810.

(75) Xiaodong, Z.; Yiyong, M.; Dongqing, W.; Fan, Z.; Xinliang, F. Two-Dimensional Soft Nanomaterials: A Fascinating World of Materials. Adv. Mater. 2015, 27, 403−427. (76) Terrones, M.; Botello-Méndez, A. R.; Campos-Delgado, J.; López-Urías, F.; Vega-Cantú, Y. I.; Rodríguez-Macías, F. J.; Elías, A. L.; Muñoz-Sandoval, E.; Cano-Márquez, A. G.; Charlier, J.-C.; Terrones, H. Graphene and Graphite Nanoribbons: Morphology, Properties, Synthesis, Defects and Applications. Nano Today 2010, 5, 351−372. (77) Jia, X.; Campos-Delgado, J.; Terrones, M.; Meunier, V.; Dresselhaus, M. S. Graphene Edges: A Review of Their Fabrication and Characterization. Nanoscale 2011, 3, 86−95. (78) Samori, P.; Palermo, V.; Feng, X. Chemical Approaches to 2D Materials. Adv. Mater. 2016, 28, 6027−6029. (79) Georgakilas, V.; Otyepka, M.; Bourlinos, A. B.; Chandra, V.; Kim, N.; Kemp, K. C.; Hobza, P.; Zboril, R.; Kim, K. S. Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications. Chem. Rev. 2012, 112, 6156−6214. (80) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5, 263. (81) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Liquid Exfoliation of Layered Materials. Science 2013, 340, 1226419. (82) Ciesielski, A.; Samori, P. Graphene via Sonication Assisted Liquid-Phase Exfoliation. Chem. Soc. Rev. 2014, 43, 381−398. (83) Parvez, K.; Yang, S.; Feng, X.; Müllen, K. Exfoliation of Graphene via Wet Chemical Routes. Synth. Met. 2015, 210, 123−132. (84) Bonaccorso, F.; Lombardo, A.; Hasan, T.; Sun, Z.; Colombo, L.; Ferrari, A. C. Production and Processing of Graphene and 2d Crystals. Mater. Today 2012, 15, 564−589. (85) Del Rio Castillo, A. E.; Pellegrini, V.; Ansaldo, A.; Ricciardella, F.; Sun, H.; Marasco, L.; Buha, J.; Dang, Z.; Gagliani, L.; Lago, E.; Bonaccorso, F. High-Yield Production of 2D Crystals by Wet-Jet Milling. Mater. Horiz. 2018, 5, 890−904. (86) Bonaccorso, F.; Bartolotta, A.; Coleman, J. N.; Backes, C. 2DCrystal-Based Functional Inks. Adv. Mater. 2016, 28, 6136−6166. (87) Tung, V. C.; Allen, M. J.; Yang, Y.; Kaner, R. B. HighThroughput Solution Processing of Large-Scale Graphene. Nat. Nanotechnol. 2009, 4, 25. (88) Li, D.; Müller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable Aqueous Dispersions of Graphene Nanosheets. Nat. Nanotechnol. 2008, 3, 101. (89) Torrisi, F.; Hasan, T.; Wu, W.; Sun, Z.; Lombardo, A.; Kulmala, T. S.; Hsieh, G.-W.; Jung, S.; Bonaccorso, F.; Paul, P. J.; Chu, D. Inkjet-Printed Graphene Electronics. ACS Nano 2012, 6, 2992−3006. (90) Secor, E. B.; Lim, S.; Zhang, H.; Frisbie, C. D.; Francis, L. F.; Hersam, M. C. Gravure Printing of Graphene for Large-Area Flexible Electronics. Adv. Mater. 2014, 26, 4533−4538. (91) You, J.; Hong, Z.; Yang, Y.; Chen, Q.; Cai, M.; Song, T.-B.; Chen, C.-C.; Lu, S.; Liu, Y.; Zhou, H.; Yang, Y. Low-Temperature Solution-Processed Perovskite Solar Cells with High Efficiency and Flexibility. ACS Nano 2014, 8, 1674−1680. (92) Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; García de Arquer, F. P.; Fan, J. Z.; Quintero-Bermudez, R.; Yuan, M.; Zhang, B.; Zhao, Y.; Fan, F. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation. Science 2017, 355, 722−726. (93) Chueh, C.-C.; Li, C.-Z.; Jen, A. K.-Y. Recent Progress and Perspective in Solution-Processed Interfacial Materials for Efficient and Stable Polymer and Organometal Perovskite Solar Cells. Energy Environ. Sci. 2015, 8, 1160−1189. (94) Singh, E.; Kim, K. S.; Yeom, G. Y.; Nalwa, H. S. Atomically Thin-Layered Molybdenum Disulfide (MoS2) for Bulk-Heterojunction Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 3223−3245. (95) Bellani, S.; Najafi, L.; Capasso, A.; Del Rio Castillo, A. E.; Antognazza, M. R.; Bonaccorso, F. Few-Layer MoS2 Flakes as a HoleSelective Layer for Solution-Processed Hybrid Organic HydrogenEvolving Photocathodes. J. Mater. Chem. A 2017, 5, 4384−4396. N


Article

ACS Nano (96) Capasso, A.; Del Rio Castillo, A. E.; Najafi, L.; Pellegrini, V.; Bonaccorso, F.; Matteocci, F.; Cinà, L.; Di Carlo, A. Spray Deposition of Exfoliated MoS2 Flakes as Hole Transport Layer in PerovskiteBased Photovoltaics. In 2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO); 2015; pp 1138−1141. (97) Kohnehpoushi, S.; Nazari, P.; Nejand, B. A.; Eskandari, M. MoS 2 : A Two-Dimensional Hole-Transporting Material for HighEfficiency, Low-Cost Perovskite Solar Cells. Nanotechnology 2018, 29, 205201. (98) Xing, G.; Wei, C.; Hai, L.; Zhongwei, W.; Zhiyuan, Z.; ShuitTong, L.; Hua, Z.; Baoquan, S. A Solution-Processed Hole Extraction Layer Made from Ultrathin MoS2 Nanosheets for Efficient Organic Solar Cells. Adv. Energy Mater. 2013, 3, 1262−1268. (99) Xing, W.; Chen, Y.; Wang, X.; Lv, L.; Ouyang, X.; Ge, Z.; Huang, H. MoS2 Quantum Dots with a Tunable Work Function for High-Performance Organic Solar Cells. ACS Appl. Mater. Interfaces 2016, 8, 26916−26923. (100) Wu, Z.; Bai, S.; Xiang, J.; Yuan, Z.; Yang, Y.; Cui, W.; Gao, X.; Liu, Z.; Jin, Y.; Sun, B. Efficient Planar Heterojunction Perovskite Solar Cells Employing Graphene Oxide as Hole Conductor. Nanoscale 2014, 6, 10505−10510. (101) Yan, K.; Wei, Z.; Li, J.; Chen, H.; Yi, Y.; Zheng, X.; Long, X.; Wang, Z.; Wang, J.; Xu, J.; Yang, S. High-Performance GrapheneBased Hole Conductor-Free Perovskite Solar Cells: Schottky Junction Enhanced Hole Extraction and Electron Blocking. Small 2015, 11, 2269−2274. (102) Palma, A. L.; Cinà, L.; Pescetelli, S.; Agresti, A.; Raggio, M.; Paolesse, R.; Bonaccorso, F.; Di Carlo, A. Reduced Graphene Oxide as Efficient and Stable Hole Transporting Material in Mesoscopic Perovskite Solar Cells. Nano Energy 2016, 22, 349−360. (103) Yeo, J.-S.; Kang, R.; Lee, S.; Jeon, Y.-J.; Myoung, N.; Lee, C.L.; Kim, D.-Y.; Yun, J.-M.; Seo, Y.-H.; Kim, S.-S.; Na, S. I. Highly Efficient and Stable Planar Perovskite Solar Cells with Reduced Graphene Oxide Nanosheets as Electrode Interlayer. Nano Energy 2015, 12, 96−104. (104) Arora, N.; Dar, M. I.; Hinderhofer, A.; Pellet, N.; Schreiber, F.; Zakeeruddin, S. M.; Grätzel, M. Perovskite Solar Cells with CuSCN Hole Extraction Layers Yield Stabilized Efficiencies Greater than 20%. Science 2017, 358, 768−771. (105) Nouri, E.; Wang, Y.-L.; Chen, Q.; Xu, J.-J.; Paterakis, G.; Dracopoulos, V.; Xu, Z.-X.; Tasis, D.; Mohammadi, M. R.; Lianos, P. Introduction of Graphene Oxide as Buffer Layer in Perovskite Solar Cells and the Promotion of Soluble N-Butyl-Substituted Copper Phthalocyanine as Efficient Hole Transporting Material. Electrochim. Acta 2017, 233, 36−43. (106) Lee, S. Y.; Kim, U. J.; Chung, J.; Nam, H.; Jeong, H. Y.; Han, G. H.; Kim, H.; Oh, H. M.; Lee, H.; Kim, H.; Roh, Y. G. Large Work Function Modulation of Monolayer MoS2 by Ambient Gases. ACS Nano 2016, 10, 6100−6107. (107) Zhou, P.; Song, X.; Yan, X.; Liu, C.; Chen, L.; Sun, Q.; Zhang, D. W. Controlling the Work Function of Molybdenum Disulfide by in Situ Metal Deposition. Nanotechnology 2016, 27, 344002. (108) Baik, S. S.; Im, S.; Choi, H. J. Work Function Tuning in TwoDimensional MoS2 Field-Effect-Transistors with Graphene and Titanium Source-Drain Contacts. Sci. Rep. 2017, 7, 45546. (109) Kim, J. H.; Lee, J.; Kim, J. H.; Hwang, C. C.; Lee, C.; Park, J. Y. Work Function Variation of MoS2 Atomic Layers Grown with Chemical Vapor Deposition: The Effects of Thickness and the Adsorption of Water/oxygen Molecules. Appl. Phys. Lett. 2015, 106, 251606. (110) Shi, Y.; Kim, K. K.; Reina, A.; Hofmann, M.; Li, L.-J.; Kong, J. Work Function Engineering of Graphene Electrode via Chemical Doping. ACS Nano 2010, 4, 2689−2694. (111) Chang, K. K.; Soon, C. K.; Young, K. S. Increased Work Function in Few-Layer Graphene Sheets via Metal Chloride Doping. Adv. Funct. Mater. 2012, 22, 4724−4731. (112) Garg, R.; Dutta, K. N.; Choudhury, R. N. Work Function Engineering of Graphene. Nanomaterials 2014, 4, 267.

(113) Sygellou, L.; Paterakis, G.; Galiotis, C.; Tasis, D. Work Function Tuning of Reduced Graphene Oxide Thin Films. J. Phys. Chem. C 2016, 120, 281−290. (114) Harwell, J. R.; Baikie, T. K.; Baikie, I. D.; Payne, J. L.; Ni, C.; Irvine, J. T. S.; Turnbull, G. A.; Samuel, I. D. W. Probing the Energy Levels of Perovskite Solar Cells via Kelvin Probe and UV Ambient Pressure Photoemission Spectroscopy. Phys. Chem. Chem. Phys. 2016, 18, 19738−19745. (115) Nguyen, W. H.; Bailie, C. D.; Unger, E. L.; McGehee, M. D. Enhancing the Hole-Conductivity of Spiro-OMeTAD without Oxygen or Lithium Salts by Using Spiro(TFSI)2 in Perovskite and Dye-Sensitized Solar Cells. J. Am. Chem. Soc. 2014, 136, 10996− 11001. (116) Saygili, Y.; Turren-Cruz, S. H.; Olthof, S.; Saes, B. W. H.; Pehlivan, I. B.; Saliba, M.; Meerholz, K.; Edvinsson, T.; Zakeeruddin, S. M.; Grätzel, M.; Correa-Baena, J. P. Planar Perovskite Solar Cells with High Open-Circuit Voltage Containing a Supramolecular Iron Complex as Hole Transport Material Dopant. ChemPhysChem 2018, 19, 1363−1370. (117) Schölin, R.; Karlsson, M. H.; Eriksson, S. K.; Siegbahn, H.; Johansson, E. M. J.; Rensmo, H. Energy Level Shifts in SpiroOMeTAD Molecular Thin Films When Adding Li-TFSI. J. Phys. Chem. C 2012, 116, 26300−26305. (118) Nardes, A. M.; Kemerink, M.; de Kok, M. M.; Vinken, E.; Maturova, K.; Janssen, R. A. J. Conductivity, Work Function, and Environmental Stability of PEDOT:PSS Thin Films Treated with Sorbitol. Org. Electron. 2008, 9, 727−734. (119) Huang, J.; Miller, P. F.; Wilson, J. S.; de Mello, A. J.; de Mello, J. C.; Bradley, D. D. C. Investigation of the Effects of Doping and Post-Deposition Treatments on the Conductivity, Morphology, and Work Function of Poly(3,4-ethylenedioxythiophene)/Poly(styrene Sulfonate) Films. Adv. Funct. Mater. 2005, 15, 290−296. (120) Hwang, J.; Amy, F.; Kahn, A. Spectroscopic Study on Sputtered PEDOT·PSS: Role of Surface PSS Layer. Org. Electron. 2006, 7, 387−396. (121) Brown, T. M.; Kim, J. S.; Friend, R. H.; Cacialli, F.; Daik, R.; Feast, W. J. Built-in Field Electroabsorption Spectroscopy of Polymer Light-Emitting Diodes Incorporating a Doped poly(3,4-Ethylene Dioxythiophene) Hole Injection Layer. Appl. Phys. Lett. 1999, 75, 1679−1681. (122) Jun, L.; Yuhua, X.; Yunxiang, G.; Dingshan, Y.; Michael, D.; Liming, D. Hole and Electron Extraction Layers Based on Graphene Oxide Derivatives for High-Performance Bulk Heterojunction Solar Cells. Adv. Mater. 2012, 24, 2228−2233. (123) Lin, Y.; Li, X.; Xie, D.; Feng, T.; Chen, Y.; Song, R.; Tian, H.; Ren, T.; Zhong, M.; Wang, K.; Zhu, H. Graphene/semiconductor Heterojunction Solar Cells with Modulated Antireflection and Graphene Work Function. Energy Environ. Sci. 2013, 6, 108−115. (124) Huang, H.; Li, Z.; She, J.; Wang, W. Oxygen Density Dependent Band Gap of Reduced Graphene Oxide. J. Appl. Phys. 2012, 111, 54317. (125) Shen, Y.; Yang, S.; Zhou, P.; Sun, Q.; Wang, P.; Wan, L.; Li, J.; Chen, L.; Wang, X.; Ding, S.; Zhang, D. W. Evolution of the BandGap and Optical Properties of Graphene Oxide with Controllable Reduction Level. Carbon 2013, 62, 157−164. (126) Ellis, J. K.; Lucero, M. J.; Scuseria, G. E. The Indirect to Direct Band Gap Transition in Multilayered MoS2 as Predicted by Screened Hybrid Density Functional Theory. Appl. Phys. Lett. 2011, 99, 261908. (127) Yun, W. S.; Han, S. W.; Hong, S. C.; Kim, I. G.; Lee, J. D. Thickness and Strain Effects on Electronic Structures of Transition Metal Dichalcogenides: 2H-MX2 Semiconductors (M = Mo, W; X = S, Se, Te). Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 85, 033305. (128) Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105, 136805. (129) Han, S. W.; Kwon, H.; Kim, S. K.; Ryu, S.; Yun, W. S.; Kim, D. H.; Hwang, J. H.; Kang, J.-S.; Baik, J.; Shin, H. J.; Hong, S. C. BandO


Article

ACS Nano Gap Transition Induced by Interlayer van Der Waals Interaction in MoS2. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 84, 045409. (130) Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics and Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat. Nanotechnol. 2012, 7, 699. (131) Kang, J.; Tongay, S.; Zhou, J.; Li, J.; Wu, J. Band Offsets and Heterostructures of Two-Dimensional Semiconductors. Appl. Phys. Lett. 2013, 102, 12111. (132) Wu, M.; Yao, X.; Hao, Y.; Dong, H.; Cheng, Y.; Liu, H.; Lu, F.; Wang, W.; Cho, K.; Wang, W.-H. Electronic Structures, Magnetic Properties and Band Alignments of 3d Transition Metal Atoms Doped Monolayer MoS2. Phys. Lett. A 2018, 382, 111−115. (133) Rasmussen, F. A.; Thygesen, K. S. Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides. J. Phys. Chem. C 2015, 119, 13169− 13183. (134) Qiu, J.; Qiu, Y.; Yan, K.; Zhong, M.; Mu, C.; Yan, H.; Yang, S. All-Solid-State Hybrid Solar Cells Based on a New Organometal Halide Perovskite Sensitizer and One-Dimensional TiO2 Nanowire Arrays. Nanoscale 2013, 5, 3245−3248. (135) Yang, G.; Tao, H.; Qin, P.; Ke, W.; Fang, G. Recent Progress in Electron Transport Layers for Efficient Perovskite Solar Cells. J. Mater. Chem. A 2016, 4, 3970−3990. (136) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Grätzel, M. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, 591. (137) Hao, F.; Stoumpos, C. C.; Chang, R. P. H.; Kanatzidis, M. G. Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells. J. Am. Chem. Soc. 2014, 136, 8094−8099. (138) Olthof, S. Research Update: The Electronic Structure of Hybrid Perovskite Layers and Their Energetic Alignment in Devices. APL Mater. 2016, 4, 91502. (139) Schulz, P.; Whittaker-Brooks, L.; MacLeod, B.; Olson, D.; Yueh-Lin, L.; Antoine, K. Electronic Level Alignment in Inverted Organometal Perovskite Solar Cells. Adv. Mater. Interfaces 2015, 2, 1400532. (140) Ratcliff, E. L.; Garcia, A.; Paniagua, S. A.; Cowan, S. R.; Giordano, A. J.; Ginley, D. S.; Marder, S. R.; Berry, J. J.; Olson, D. C. Investigating the Influence of Interfacial Contact Properties on Open Circuit Voltages in Organic Photovoltaic Performance: Work Function Versus Selectivity. Adv. Energy Mater. 2013, 3, 647−656. (141) Steim, R.; Choulis, S. A.; Schilinsky, P.; Brabec, C. J. Interface Modification for Highly Efficient Organic Photovoltaics. Appl. Phys. Lett. 2008, 92, 93303. (142) Zhong, H.; Quhe, R.; Wang, Y.; Ni, Z.; Ye, M.; Song, Z.; Pan, Y.; Yang, J.; Yang, L.; Lei, M.; Shi, J. Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations. Sci. Rep. 2016, 6, 21786. (143) Yun, J.-M.; Noh, Y.-J.; Yeo, J.-S.; Go, Y.-J.; Na, S.-I.; Jeong, H.G.; Kim, J.; Lee, S.; Kim, S.-S.; Koo, H. Y.; Kim, T. W. Efficient WorkFunction Engineering of Solution-Processed MoS2 Thin-Films for Novel Hole and Electron Transport Layers Leading to HighPerformance Polymer Solar Cells. J. Mater. Chem. C 2013, 1, 3777−3783. (144) Najafi, L.; Bellani, S.; Martín-García, B.; Oropesa-Nuñez, R.; Del Rio Castillo, A. E.; Prato, M.; Moreels, I.; Bonaccorso, F. Solution-Processed Hybrid Graphene Flake/2H-MoS2 Quantum Dot Heterostructures for Efficient Electrochemical Hydrogen Evolution. Chem. Mater. 2017, 29, 5782−5786. (145) Sun, Y.; Takacs, C. J.; Cowan, S. R.; Seo, J. H.; Gong, X.; Roy, A.; Heeger, A. J. Efficient, Air-Stable Bulk Heterojunction Polymer Solar Cells Using MoOx as the Anode Interfacial Layer. Adv. Mater. 2011, 23, 2226−2230. (146) Fumagalli, F.; Bellani, S.; Schreier, M.; Leonardi, S.; Rojas, H. C.; Ghadirzadeh, A.; Tullii, G.; Savoini, A.; Marra, G.; Meda, L.; Grätzel, M.; Lanzani, G.; Mayer, M. T.; Antognazza, M. R.; Di Fonzo,

F. Hybrid Organic−inorganic H2-Evolving Photocathodes: Understanding the Route towards High Performance Organic Photoelectrochemical Water Splitting. J. Mater. Chem. A 2016, 4, 2178− 2187. (147) Chen, L.-M.; Xu, Z.; Hong, Z.; Yang, Y. Interface Investigation and Engineering − Achieving High Performance Polymer Photovoltaic Devices. J. Mater. Chem. 2010, 20, 2575. (148) Lu, C.-P.; Li, G.; Mao, J.; Wang, L.-M.; Andrei, E. Y. Bandgap, Mid-Gap States, and Gating Effects in MoS2. Nano Lett. 2014, 14, 4628−4633. (149) Fivaz, R.; Mooser, E. Mobility of Charge Carriers in Semiconducting Layer Structures. Phys. Rev. 1967, 163, 743−755. (150) El-Mahalawy, S.; Evans, B. Temperature Dependence of the Electrical Conductivity and Hall Coefficient in 2H-MoS2, MoSe2, WSe2, and MoTe2. Phys. Status Solidi B 2018, 79, 713−722. (151) Dolui, K.; Rungger, I.; Sanvito, S. Origin of the N-Type and PType Conductivity of MoS2Monolayers on a SiO2 Substrate. Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 165402. (152) Yuan, S.; Roldán, R.; Katsnelson, M. I.; Guinea, F. Effect of Point Defects on the Optical and Transport Properties of MoS2 and WS2. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 90, 041402. (153) Vancsó, P.; Magda, G. Z.; Pető , J.; Noh, J.-Y.; Kim, Y.-S.; Hwang, C.; Biró, L. P.; Tapasztó, L. The Intrinsic Defect Structure of Exfoliated MoS2 Single Layers Revealed by Scanning Tunneling Microscopy. Sci. Rep. 2016, 6, 29726. (154) Cho, K.; Min, M.; Kim, T.-Y.; Jeong, H.; Pak, J.; Kim, J.-K.; Jang, J.; Yun, S. J.; Lee, Y. H.; Hong, W.-K.; Lee, T. Electrical and Optical Characterization of MoS2 with Sulfur Vacancy Passivation by Treatment with Alkanethiol Molecules. ACS Nano 2015, 9, 8044− 8053. (155) Liu, D.; Guo, Y.; Fang, L.; Robertson, J. Sulfur Vacancies in Monolayer MoS2 and Its Electrical Contacts. Appl. Phys. Lett. 2013, 103, 183113. (156) Le, D.; Rawal, T. B.; Rahman, T. S. Single-Layer MoS2 with Sulfur Vacancies: Structure and Catalytic Application. J. Phys. Chem. C 2014, 118, 5346−5351. (157) Qiu, H.; Xu, T.; Wang, Z.; Ren, W.; Nan, H.; Ni, Z.; Chen, Q.; Yuan, S.; Miao, F.; Song, F.; Long, G. Hopping Transport through Defect-Induced Localized States in Molybdenum Disulphide. Nat. Commun. 2013, 4, 2642. (158) Fabbri, F.; Rotunno, E.; Cinquanta, E.; Campi, D.; Bonnini, E.; Kaplan, D.; Lazzarini, L.; Bernasconi, M.; Ferrari, C.; Longo, M.; Nicotra, G. Novel near-Infrared Emission from Crystal Defects in MoS2Multilayer Flakes. Nat. Commun. 2016, 7, 13044. (159) Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H. Single-Layer MoS2 Phototransistors. ACS Nano 2012, 6, 74−80. (160) Yung-Chang, L.; O, D. D.; Hannu-Pekka, K.; Yoshiko, N.; V, K. A.; Ying-Sheng, H.; Kazu, S. Properties of Individual Dopant Atoms in Single-Layer MoS2: Atomic Structure, Migration, and Enhanced Reactivity. Adv. Mater. 2014, 26, 2857−2861. (161) Baugher, B. W. H.; Churchill, H. O. H.; Yang, Y.; JarilloHerrero, P. Intrinsic Electronic Transport Properties of High-Quality Monolayer and Bilayer MoS2. Nano Lett. 2013, 13, 4212−4216. (162) McDonnell, S.; Addou, R.; Buie, C.; Wallace, R. M.; Hinkle, C. L. Defect-Dominated Doping and Contact Resistance in MoS2. ACS Nano 2014, 8, 2880−2888. (163) Zhou, W.; Zou, X.; Najmaei, S.; Liu, Z.; Shi, Y.; Kong, J.; Lou, J.; Ajayan, P. M.; Yakobson, B. I.; Idrobo, J.-C. Intrinsic Structural Defects in Monolayer Molybdenum Disulfide. Nano Lett. 2013, 13, 2615−2622. (164) Santosh, K. C.; Longo, R. C; Addou, R.; Wallace, R. M; Cho, K. Impact of Intrinsic Atomic Defects on the Electronic Structure of MoS 2 Monolayers. Nanotechnology 2014, 25, 375703. (165) Zhao, Y.; Nardes, A. M.; Zhu, K. Solid-State Mesostructured Perovskite CH3NH3PbI3 Solar Cells: Charge Transport, Recombination, and Diffusion Length. J. Phys. Chem. Lett. 2014, 5, 490−494. (166) Martín-García, B.; Polovitsyn, A.; Prato, M.; Moreels, I. Efficient Charge Transfer in Solution-Processed PbS Quantum Dot− P


Article

ACS Nano reduced Graphene Oxide Hybrid Materials. J. Mater. Chem. C 2015, 3, 7088−7095. (167) Hou, S.; Su, S.; Kasner, M. L.; Shah, P.; Patel, K.; Madarang, C. J. Formation of Highly Stable Dispersions of Silane-Functionalized Reduced Graphene Oxide. Chem. Phys. Lett. 2010, 501, 68−74. (168) Yao, H.; Jin, L.; Sue, H.-J.; Sumi, Y.; Nishimura, R. Facile Decoration of Au Nanoparticles on Reduced Graphene Oxide Surfaces via a One-Step Chemical Functionalization Approach. J. Mater. Chem. A 2013, 1, 10783. (169) Chen, X.; Berner, N. C.; Backes, C.; Duesberg, G. S.; McDonald, A. R. Functionalization of Two-Dimensional MoS2 : On the Reaction Between MoS2 and Organic Thiols. Angew. Chem., Int. Ed. 2016, 55, 5803−5808. (170) Förster, A.; Gemming, S.; Seifert, G.; Tománek, D. Chemical and Electronic Repair Mechanism of Defects in MoS2Monolayers. ACS Nano 2017, 11, 9989−9996. (171) Ding, Q.; Czech, K. J.; Zhao, Y.; Zhai, J.; Hamers, R. J.; Wright, J. C.; Jin, S. Basal-Plane Ligand Functionalization on Semiconducting 2H-MoS2Monolayers. ACS Appl. Mater. Interfaces 2017, 9, 12734−12742. (172) Green, A. A.; Hersam, M. C. Solution Phase Production of Graphene with Controlled Thickness via Density Differentiation. Nano Lett. 2009, 9, 4031−4036. (173) Sun, X.; Luo, D.; Liu, J.; Evans, D. G. Monodisperse Chemically Modified Graphene Obtained by Density Gradient Ultracentrifugal Rate Separation. ACS Nano 2010, 4, 3381−3389. (174) Björkman, T.; Gulans, A.; Krasheninnikov, A. V.; Nieminen, R. M. Van Der Waals Bonding in Layered Compounds from Advanced Density-Functional First-Principles Calculations. Phys. Rev. Lett. 2012, 108, 235502. (175) Toulhoat, P. R.; Raybaud, P.; Kresse, G.; Hafner, J. Ab Initio Density Functional Studies of Transition-Metal Sulphides: I. Crystal Structure and Cohesive Properties. J. Phys.: Condens. Matter 1997, 9, 11085. (176) Bučko, T.; Hafner, J.; Lebègue, S.; Á ngyán, J. G. Improved Description of the Structure of Molecular and Layered Crystals: Ab Initio DFT Calculations with van Der Waals Corrections. J. Phys. Chem. A 2010, 114, 11814−11824. (177) Jawaid, A.; Nepal, D.; Park, K.; Jespersen, M.; Qualley, A.; Mirau, P.; Drummy, L. F.; Vaia, R. A. Mechanism for Liquid Phase Exfoliation of MoS2. Chem. Mater. 2016, 28, 337−348. (178) Shen, J.; He, Y.; Wu, J.; Gao, C.; Keyshar, K.; Zhang, X.; Yang, Y.; Ye, M.; Vajtai, R.; Lou, J.; Ajayan, P. M. Liquid Phase Exfoliation of Two-Dimensional Materials by Directly Probing and Matching Surface Tension Components. Nano Lett. 2015, 15, 5449−5454. (179) Bonaccorso, F.; Zerbetto, M.; Ferrari, A. C.; Amendola, V. Sorting Nanoparticles by Centrifugal Fields in Clean Media. J. Phys. Chem. C 2013, 117, 13217−13229. (180) Gao, X.; Jang, J.; Nagase, S. Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design. J. Phys. Chem. C 2010, 114, 832− 842. (181) Pei, S.; Cheng, H.-M. The Reduction of Graphene Oxide. Carbon 2012, 50, 3210−3228. (182) Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339. (183) Bellani, S.; Najafi, L.; Martín-García, B.; Ansaldo, A.; Del Rio Castillo, A. E.; Prato, M.; Moreels, I.; Bonaccorso, F. Graphene-Based Hole-Selective Layers for High-Efficiency, Solution-Processed, LargeArea, Flexible, Hydrogen-Evolving Organic Photocathodes. J. Phys. Chem. C 2017, 121, 21887−21903. (184) Zhang, X.; Coleman, A. C.; Katsonis, N.; Browne, W. R.; van Wees, B. J.; Feringa, B. L. Dispersion of Graphene in Ethanol Using a Simple Solvent Exchange Method. Chem. Commun. 2010, 46, 7539− 7541. (185) Sun, H.; Del Rio Castillo, A. E.; Monaco, S.; Capasso, A.; Ansaldo, A.; Prato, M.; Dinh, D. A.; Pellegrini, V.; Scrosati, B.; Manna, L.; Bonaccorso, F. Binder-Free Graphene as an Advanced Anode for Lithium Batteries. J. Mater. Chem. A 2016, 4, 6886−6895.

(186) Gao, W. The Chemistry of Graphene Oxide: Graphene Oxide: Reduction Recipes, Spectroscopy, and Applications; Gao, W., Ed.; Springer International Publishing: Cham, 2015; pp 61−95. (187) Pham, N. P.; Burghartz, J. N.; Sarro, P. M. Spray Coating of Photoresist for Pattern Transfer on High Topography Surfaces. J. Micromech. Microeng. 2005, 15, 691. (188) Song, Z.; McElvany, C. L.; Phillips, A. B.; Celik, I.; Krantz, P. W.; Watthage, S. C.; Liyanage, G. K.; Apul, D.; Heben, M. J. A Technoeconomic Analysis of Perovskite Solar Module Manufacturing with Low-Cost Materials and Techniques. Energy Environ. Sci. 2017, 10, 1297−1305. (189) Yang, Z.; Zhang, S.; Li, L.; Chen, W. Research Progress on Large-Area Perovskite Thin Films and Solar Modules. J. Materiomics 2017, 3, 231−244. (190) Ono, L. K.; Park, N.-G.; Zhu, K.; Huang, W.; Qi, Y. Perovskite Solar CellsTowards Commercialization. ACS Energy Lett. 2017, 2, 1749−1751. (191) Berry, J. J.; van de Lagemaat, J.; Al-Jassim, M. M.; Kurtz, S.; Yan, Y.; Zhu, K. Perovskite Photovoltaics: The Path to a Printable Terawatt-Scale Technology. ACS Energy Lett. 2017, 2, 2540−2544. (192) Lee, C.; Yan, H.; Brus, L. E.; Heinz, T. F.; Hone, J.; Ryu, S. Anomalous Lattice Vibrations of Single- and Few-Layer MoS2. ACS Nano 2010, 4, 2695−2700. (193) Huang, Y.; Wu, J.; Hwang, K. C. Thickness of Graphene and Single-Wall Carbon Nanotubes. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 74, 245413. (194) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666−669. (195) Baker, M. A.; Gilmore, R.; Lenardi, C.; Gissler, W. XPS Investigation of Preferential Sputtering of S from MoS2 and Determination of MoSx Stoichiometry from Mo and S Peak Positions. Appl. Surf. Sci. 1999, 150, 255−262. (196) Lee, Y. H.; Zhang, X. Q.; Zhang, W.; Chang, M. T.; Lin, C. T.; Chang, K. D.; Yu, Y. C.; Wang, J. T. W.; Chang, C. S.; Li, L. J.; Lin, T. W. Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition. Adv. Mater. 2012, 24, 2320−2325. (197) Weber, T.; Muijsers, J. C.; van Wolput, J. H. M. C.; Verhagen, C. P. J.; Niemantsverdriet, J. W. Basic Reaction Steps in the Sulfidation of Crystalline MoO3 to MoS2, As Studied by X-Ray Photoelectron and Infrared Emission Spectroscopy. J. Phys. Chem. 1996, 100, 14144−14150. (198) Najafi, L.; Bellani, S.; Oropesa-Nuñez, R.; Ansaldo, A.; Prato, M.; Castillo, A. E.D.R.; Bonaccorso, F. Engineered MoSe2 -Based Heterostructures for Efficient Electrochemical Hydrogen Evolution Reaction. Adv. Energy Mater. 2018, 8, 1703212. (199) Bonaccorso, F.; Colombo, L.; Yu, G.; Stoller, M.; Tozzini, V.; Ferrari, A. C.; Ruoff, R. S.; Pellegrini, V. Graphene, Related TwoDimensional Crystals, and Hybrid Systems for Energy Conversion and Storage. Science 2015, 347, 1246501. (200) Yang, D.; Velamakanni, A.; Bozoklu, G.; Park, S.; Stoller, M.; Piner, R. D.; Stankovich, S.; Jung, I.; Field, D. A.; Ventrice, C. A.; Ruoff, R. S. Chemical Analysis of Graphene Oxide Films after Heat and Chemical Treatments by X-Ray Photoelectron and Micro-Raman Spectroscopy. Carbon 2009, 47, 145−152. (201) Dong, X.; Su, C.-Y.; Zhang, W.; Zhao, J.; Ling, Q.; Huang, W.; Chen, P.; Li, L.-J. Ultra-Large Single-Layer Graphene Obtained from Solution Chemical Reduction and Its Electrical Properties. Phys. Chem. Chem. Phys. 2010, 12, 2164−2169. (202) Becerril, H. A.; Stoltenberg, R. M.; Tang, M. L.; Roberts, M. E.; Liu, Z.; Chen, Y.; Kim, D. H.; Lee, B.-L.; Lee, S.; Bao, Z. Fabrication and Evaluation of Solution-Processed Reduced Graphene Oxide Electrodes for P- and N-Channel Bottom-Contact Organic Thin-Film Transistors. ACS Nano 2010, 4, 6343−6352. (203) Ganguly, A.; Sharma, S.; Papakonstantinou, P.; Hamilton, J. Probing the Thermal Deoxygenation of Graphene Oxide Using HighResolution In Situ X-Ray-Based Spectroscopies. J. Phys. Chem. C 2011, 115, 17009−17019. Q


Article

ACS Nano (204) Gao, W.; Alemany, L. B.; Ci, L.; Ajayan, P. M. New Insights into the Structure and Reduction of Graphite Oxide. Nat. Chem. 2009, 1, 403. (205) Johnson, P. A.; Levicky, R. X-Ray Photoelectron Spectroscopy and Differential Capacitance Study of Thiol-Functional Polysiloxane Films on Gold Supports. Langmuir 2004, 20, 9621−9627. (206) Rodriguez, J. A.; Jirsak, T.; Freitag, A.; Hanson, J. C.; Larese, J. Z.; Chaturvedi, S. Interaction of SO2 with CeO2 and Cu/CeO2 Catalysts: Photoemission, XANES and TPD Studies. Catal. Lett. 1999, 62, 113−119. (207) Lee, C. Y.; Le, Q. V.; Kim, C.; Kim, S. Y. Use of SilaneFunctionalized Graphene Oxide in Organic Photovoltaic Cells and Organic Light-Emitting Diodes. Phys. Chem. Chem. Phys. 2015, 17, 9369−9374. (208) Konios, D.; Stylianakis, M. M.; Stratakis, E.; Kymakis, E. Dispersion Behaviour of Graphene Oxide and Reduced Graphene Oxide. J. Colloid Interface Sci. 2014, 430, 108−112. (209) Wang, S.; Zhang, Y.; Abidi, N.; Cabrales, L. Wettability and Surface Free Energy of Graphene Films. Langmuir 2009, 25, 11078− 11081. (210) Jiménez Sandoval, S.; Yang, D.; Frindt, R. F.; Irwin, J. C. Raman Study and Lattice Dynamics of Single Molecular Layers of MoS2. Phys. Rev. B: Condens. Matter Mater. Phys. 1991, 44, 3955− 3962. (211) Kopaczek, J.; Polak, M. P.; Scharoch, P.; Wu, K.; Chen, B.; Tongay, S.; Kudrawiec, R. Direct Optical Transitions at K- and HPoint of Brillouin Zone in Bulk MoS2, MoSe2, WS2, and WSe2. J. Appl. Phys. 2016, 119, 235705. (212) Cheiwchanchamnangij, T.; Lambrecht, W. R. L. Quasiparticle Band Structure Calculation of Monolayer, Bilayer, and Bulk MoS2. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 85, 205302. (213) Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M.; Chhowalla, M. Photoluminescence from Chemically Exfoliated MoS2. Nano Lett. 2011, 11, 5111−5116. (214) Zhang, H.; Lu, S. B.; Zheng, J.; Du, J.; Wen, S. C.; Tang, D. Y.; Loh, K. P. Molybdenum Disulfide (MoS2) as a Broadband Saturable Absorber for Ultra-Fast Photonics. Opt. Express 2014, 22, 7249− 7260. (215) Gan, Z. X.; Liu, L. Z.; Wu, H. Y.; Hao, Y. L.; Shan, Y.; Wu, X. L.; Chu, P. K. Quantum Confinement Effects across Two-Dimensional Planes in MoS2 Quantum Dots. Appl. Phys. Lett. 2015, 106, 233113. (216) Dong, H. H.; Ju, H. D.; Seob, C. J.; Minsu, P.; Seok, S. T. Dual Role of Blue Luminescent MoS2 Quantum Dots in Fluorescence Resonance Energy Transfer Phenomenon. Small 2014, 10, 3858− 3862. (217) Mukherjee, S.; Maiti, R.; Katiyar, A. K.; Das, S.; Ray, S. K. Novel Colloidal MoS2 Quantum Dot Heterojunctions on Silicon Platforms for Multifunctional Optoelectronic Devices. Sci. Rep. 2016, 6, 29016. (218) Gan, Z.; Xu, H.; Hao, Y. Mechanism for Excitation-Dependent Photoluminescence from Graphene Quantum Dots and Other Graphene Oxide Derivates: Consensus, Debates and Challenges. Nanoscale 2016, 8, 7794−7807. (219) Gopalakrishnan, D.; Damien, D.; Li, B.; Gullappalli, H.; Pillai, V. K.; Ajayan, P. M.; Shaijumon, M. M. Electrochemical Synthesis of Luminescent MoS2 Quantum Dots. Chem. Commun. 2015, 51, 6293− 6296. (220) Tauc, J. Optical Properties and Electronic Structure of Amorphous Ge and Si. Mater. Res. Bull. 1968, 3, 37−46. (221) Pankove, J. I.; Kiewit, D. A. Optical Processes in Semiconductors. J. Electrochem. Soc. 1972, 5, 156C−156C. (222) Mague, J. T. Gmelin Handbook of Inorganic Chemistry, 8th ed.; Rh Organometallics, 1984. (223) Li, T.; Galli, G. Electronic Properties of MoS2 Nanoparticles. J. Phys. Chem. C 2007, 111, 16192−16196. (224) Lebègue, S.; Eriksson, O. Electronic Structure of TwoDimensional Crystals from Ab Initio Theory. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 115409.

(225) Splendiani, A.; Sun, L.; Zhang, Y.; Li, T.; Kim, J.; Chim, C.-Y.; Galli, G.; Wang, F. Emerging Photoluminescence in Monolayer MoS2. Nano Lett. 2010, 10, 1271−1275. (226) Feng, Y.; Lin, S.; Huang, S.; Shrestha, S.; Conibeer, G. Can. Tauc Plot Extrapolation Be Used for Direct-Band-Gap Semiconductor Nanocrystals? J. Appl. Phys. 2015, 117, 125701. (227) Hao, H.; Cuicui, D.; Hongyan, S.; Xun, F.; Jin, L.; Yanlei, T.; Wenbo, S. Water-Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence. Part. Part. Syst. Charact. 2015, 32, 72−79. (228) Sun, Y.; Takacs, C. J.; Cowan, S. R.; Seo, J. H.; Gong, X.; Roy, A.; Heeger, A. J. Efficient, Air-Stable Bulk Heterojunction Polymer Solar Cells Using MoOx as the Anode Interfacial Layer. Adv. Mater. 2011, 23, 2226−2230. (229) Kröger, M.; Hamwi, S.; Meyer, J.; Riedl, T.; Kowalsky, W.; Kahn, A. Role of the Deep-Lying Electronic States of MoO3 in the Enhancement of Hole-Injection in Organic Thin Films. Appl. Phys. Lett. 2009, 95, 123301. (230) Balis, N.; Stratakis, E.; Kymakis, E. Graphene and Transition Metal Dichalcogenide Nanosheets as Charge Transport Layers for Solution Processed Solar Cells. Mater. Today 2016, 19, 580−594. (231) Agresti, A.; Pescetelli, S.; Najafi, L.; Del Rio Castillo, A. E.; Oropesa-Nuñez, R.; Busby, Y.; Bonaccorso, F.; Di Carlo, A. Graphene and Related 2D Materials for High Efficient and Stable Perovskite Solar Cells. In 2017 IEEE 17th International Conference on Nanotechnology (IEEE-NANO); 2017; pp 145−150. (232) Lin, Q.; Armin, A.; Nagiri, R. C. R.; Burn, P. L.; Meredith, P. Electro-Optics of Perovskite Solar Cells. Nat. Photonics 2015, 9, 106. (233) Greiner, M. T.; Lu, Z.-H. Thin-Film Metal Oxides in Organic Semiconductor Devices: Their Electronic Structures, Work Functions and Interfaces. NPG Asia Mater. 2013, 5, e55. (234) Tress, W.; Marinova, N.; Moehl, T.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Gratzel, M. Understanding the Rate-Dependent J-V Hysteresis, Slow Time Component, and Aging in CH3NH3PbI3 Perovskite Solar Cells: The Role of a Compensated Electric Field. Energy Environ. Sci. 2015, 8, 995−1004. (235) Zhao, Y.; Liang, C.; Zhang, H.; Li, D.; Tian, D.; Li, G.; Jing, X.; Zhang, W.; Xiao, W.; Liu, Q.; Zhang, F. Anomalously Large Interface Charge in Polarity-Switchable Photovoltaic Devices: An Indication of Mobile Ions in Organic-Inorganic Halide Perovskites. Energy Environ. Sci. 2015, 8, 1256−1260. (236) Elumalai, N. K.; Uddin, A. Hysteresis in Organic-Inorganic Hybrid Perovskite Solar Cells. Sol. Energy Mater. Sol. Cells 2016, 157, 476−509. (237) Chen, B.; Yang, M.; Priya, S.; Zhu, K. Origin of J−V Hysteresis in Perovskite Solar Cells. J. Phys. Chem. Lett. 2016, 7, 905− 917. (238) Jiménez-López, J.; Cambarau, W.; Cabau, L.; Palomares, E. Charge Injection, Carriers Recombination and HOMO Energy Level Relationship in Perovskite Solar Cells. Sci. Rep. 2017, 7, 6101. (239) Docampo, P.; Ball, J. M.; Darwich, M.; Eperon, G. E.; Snaith, H. J. Efficient Organometal Trihalide Perovskite Planar-Heterojunction Solar Cells on Flexible Polymer Substrates. Nat. Commun. 2013, 4, 2761. (240) Bhosale, J. S.; Moore, J. E.; Wang, X.; Bermel, P.; Lundstrom, M. S. Steady-State Photoluminescent Excitation Characterization of Semiconductor Carrier Recombination. Rev. Sci. Instrum. 2016, 87, 13104. (241) Chang, L.; Kai, W.; Pengcheng, D.; Chao, Y.; Tianyu, M.; Xiong, G. Efficient Solution-Processed Bulk Heterojunction Perovskite Hybrid Solar Cells. Adv. Energy Mater. 2015, 5, 1402024. (242) Wang, X.; Bhosale, J.; Moore, J.; Kapadia, R.; Bermel, P.; Javey, A.; Lundstrom, M. Photovoltaic Material Characterization With Steady State and Transient Photoluminescence. IEEE J. Photovolt. 2015, 5, 282−287. (243) Ginger, D. S.; Greenham, N. C. Photoinduced Electron Transfer from Conjugated Polymers to CdSe Nanocrystals. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 10622−10629. R


Article

ACS Nano (244) Domanski, K.; Correa-Baena, J.-P.; Mine, N.; Nazeeruddin, M. K.; Abate, A.; Saliba, M.; Tress, W.; Hagfeldt, A.; Grätzel, M. Not All That Glitters Is Gold: Metal-Migration-Induced Degradation in Perovskite Solar Cells. ACS Nano 2016, 10, 6306−6314. (245) Park, N.-G.; Grätzel, M.; Miyasaka, T.; Zhu, K.; Emery, K. Towards Stable and Commercially Available Perovskite Solar Cells. Nat. Energy 2016, 1, 16152. (246) Wang, D.; Wright, M.; Elumalai, N. K.; Uddin, A. Stability of Perovskite Solar Cells. Sol. Energy Mater. Sol. Cells 2016, 147, 255− 275. (247) Qin, X.; Zhao, Z.; Wang, Y.; Wu, J.; Jiang, Q.; You, J. Recent Progress in Stability of Perovskite Solar Cells. J. Semicond. 2017, 38, 11002. (248) Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal Halide Perovskite Solar Cells: Degradation and Stability. Energy Environ. Sci. 2016, 9, 323−356. (249) Wang, Q.; Chen, B.; Liu, Y.; Deng, Y.; Bai, Y.; Dong, Q.; Huang, J. Scaling Behavior of Moisture-Induced Grain Degradation in Polycrystalline Hybrid Perovskite Thin Films. Energy Environ. Sci. 2017, 10, 516−522. (250) Han, Y.; Meyer, S.; Dkhissi, Y.; Weber, K.; Pringle, J. M.; Bach, U.; Spiccia, L.; Cheng, Y.-B. Degradation Observations of Encapsulated Planar CH3NH3PbI3 Perovskite Solar Cells at High Temperatures and Humidity. J. Mater. Chem. A 2015, 3, 8139−8147. (251) Bryant, D.; Aristidou, N.; Pont, S.; Sanchez-Molina, I.; Chotchunangatchaval, T.; Wheeler, S.; Durrant, J. R.; Haque, S. A. Light and Oxygen Induced Degradation Limits the Operational Stability of Methylammonium Lead Triiodide Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 1655−1660. (252) Aristidou, N.; Sanchez-Molina, I.; Chotchuangchutchaval, T.; Brown, M.; Martinez, L.; Rath, T.; Haque, S. A. The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers. Angew. Chem. 2015, 127, 8326−8330. (253) Pearson, A. J.; Eperon, G. E.; Hopkinson, P. E.; Habisreutinger, S. N.; Wang, J. T.-W.; Snaith, H. J.; Greenham, N. C. Oxygen Degradation in Mesoporous Al2O3/CH3NH3PbI3‑xClx Perovskite Solar Cells: Kinetics and Mechanisms. Adv. Energy Mater. 2016, 6, 1600014. (254) Nie, W.; Blancon, J.-C.; Neukirch, A. J.; Appavoo, K.; Tsai, H.; Chhowalla, M.; Alam, M. A.; Sfeir, M. Y.; Katan, C.; Even, J.; Tretiak, S. Light-Activated Photocurrent Degradation and Self-Healing in Perovskite Solar Cells. Nat. Commun. 2016, 7, 11574. (255) Docampo, P.; Bein, T. A Long-Term View on Perovskite Optoelectronics. Acc. Chem. Res. 2016, 49, 339−346. (256) Conings, B.; Drijkoningen, J.; Gauquelin, N.; Babayigit, A.; D’Haen, J.; D’Olieslaeger, L.; Ethirajan, A.; Verbeeck, J.; Manca, J.; Mosconi, E.; De Angelis, F. Intrinsic Thermal Instability of Methylammonium Lead Trihalide Perovskite. Adv. Energy Mater. 2015, 5, 1500477. (257) Juarez-Perez, E. J.; Hawash, Z.; Raga, S. R.; Ono, L. K.; Qi, Y. Thermal Degradation of CH3NH3PbI3 Perovskite into NH3 and CH3I Gases Observed by Coupled Thermogravimetry-Mass Spectrometry Analysis. Energy Environ. Sci. 2016, 9, 3406−3410. (258) Qiu, L.; Ono, L. K.; Qi, Y. Advances and Challenges to the Commercialization of Organic−inorganic Halide Perovskite Solar Cell Technology. Mater. Today Energy 2018, 7, 169−189. (259) Slavney, A. H.; Smaha, R. W.; Smith, I. C.; Jaffe, A.; Umeyama, D.; Karunadasa, H. I. Chemical Approaches to Addressing the Instability and Toxicity of Lead−Halide Perovskite Absorbers. Inorg. Chem. 2017, 56, 46−55. (260) McMeekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Hörantner, M. T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; Johnston, M. B. A Mixed-Cation Lead Mixed-Halide Perovskite Absorber for Tandem Solar Cells. Science 2016, 351, 151− 155. (261) Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Grätzel, M. Cesium-Containing Triple Cation Perovskite

Solar Cells: Improved Stability, Reproducibility and High Efficiency. Energy Environ. Sci. 2016, 9, 1989−1997. (262) Saliba, M.; Matsui, T.; Domanski, K.; Seo, J.-Y.; Ummadisingu, A.; Zakeeruddin, S. M.; Correa-Baena, J.-P.; Tress, W. R.; Abate, A.; Hagfeldt, A.; Grätzel, M. Incorporation of Rubidium Cations into Perovskite Solar Cells Improves Photovoltaic Performance. Science 2016, 354, 206−209. (263) Busby, Y.; Agresti, A.; Pescetelli, S.; Di Carlo, A.; Noel, C.; Pireaux, J.-J.; Houssiau, L. Aging Effects in Interface-Engineered Perovskite Solar Cells with 2D Nanomaterials: A Depth Profile Analysis. Mater. Today Energy 2018, 9, 1−10. (264) Jiangwei, L.; Qingshun, D.; Nan, L.; Liduo, W. Direct Evidence of Ion Diffusion for the Silver-Electrode-Induced Thermal Degradation of Inverted Perovskite Solar Cells. Adv. Energy Mater. 2017, 7, 1602922. (265) Cacovich, S.; Cina, L.; Matteocci, F.; Divitini, G.; Midgley, P. A.; Di Carlo, A.; Ducati, C. Gold and Iodine Diffusion in Large Area Perovskite Solar Cells under Illumination. Nanoscale 2017, 9, 4700− 4706. (266) Capasso, A.; Matteocci, F.; Najafi, L.; Prato, M.; Buha, J.; Cinà, L.; Pellegrini, V.; Di Carlo, A.; Bonaccorso, F. Few-Layer MoS2 Flakes as Active Buffer Layer for Stable Perovskite Solar Cells. Adv. Energy Mater. 2016, 6, 1600920. (267) Taheri, B.; Nia, N. Y.; Agresti, A.; Pescetelli, S.; Ciceroni, C.; Castillo, A. E. D. R.; Cinà, L.; Bellani, S.; Bonaccorso, F.; Di Carlo, A. Graphene-Engineered Automated Sprayed Mesoscopic Structure for Perovskite Device Scaling-Up. 2D Mater. 2018, DOI: 10.1088/20531583/aad983. (268) Reese, M. O.; Gevorgyan, S. A.; Jørgensen, M.; Bundgaard, E.; Kurtz, S. R.; Ginley, D. S.; Olson, D. C.; Lloyd, M. T.; Morvillo, P.; Katz, E. A.; Elschner, A. Consensus Stability Testing Protocols for Organic Photovoltaic Materials and Devices. Sol. Energy Mater. Sol. Cells 2011, 95, 1253−1267. (269) Matteocci, F.; Cinà, L.; Lamanna, E.; Cacovich, S.; Divitini, G.; Midgley, P. A.; Ducati, C.; Di Carlo, A. Encapsulation for LongTerm Stability Enhancement of Perovskite Solar Cells. Nano Energy 2016, 30, 162−172. (270) Matteocci, F.; Busby, Y.; Pireaux, J.-J.; Divitini, G.; Cacovich, S.; Ducati, C.; Di Carlo, A. Interface and Composition Analysis on Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 26176− 26183. (271) Petridis, C.; Kakavelakis, G.; Kymakis, E. Renaissance of Graphene-Related Materials in Photovoltaics due to the Emergence of Metal Halide Perovskite Solar Cells. Energy Environ. Sci. 2018, 11, 1030−1061. (272) Reese, M. O.; Dameron, A. A.; Kempe, M. D. Quantitative Calcium Resistivity Based Method for Accurate and Scalable Water Vapor Transmission Rate Measurement. Rev. Sci. Instrum. 2011, 82, 85101.

S


Graphene Hybrids for Advanced Interface

Recommend Documents